[1] Z. Frolík: Structure projective and structure inductive presheaves. Celebrazioni archimedee del secolo XX. Simposio di topologia.
[2] E. Čech:
Topological spaces. Prague 1966.
MR 0211373
[4] J. Pechanec-Drahoš:
Modifications of closure collections. Czech. Math. Journal, 21 (96), (1971), 577-589.
MR 0487957
[5] J. Pechanec-Drahoš:
Representations of presheaves of closure spaces. Czech. Math. Journal, 22 (97), (1972), No 1.
MR 0307143